The present disclosure relates to subject matter contained in Japanese Patent Application No. 2001-183961 filed Jun. 18, 2001, which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a variable displacement pump used as a fluid pressure source of a power steering apparatus for reducing handle operation force of an automobile, and particularly to a control apparatus of the variable displacement pump for power steering apparatus, the control apparatus for controlling a discharge flow rate of the variable displacement pump in response to a steering speed.
2. Description of the Related Art
A fluid pressure pump used in a power steering apparatus is required that a sufficient amount of pressure fluid can be fed to a power cylinder of the power steering apparatus in order to obtain steering auxiliary force corresponding to a steering state at the time of steering operation of a steering handle (so-called the time of steering). On the contrary, at the time of no steering such as the time of straight driving of a vehicle, it is practically unnecessary to feed the pressure fluid to the power steering apparatus. Also, this pump for the power steering apparatus is desired that driving stability at the time of straight driving at high speed can be ensured by decreasing the amount of feeding of the pressure fluid at the time of high speed driving to be less than the amount of feeding of the pressure fluid during a stop of the vehicle or at the time of low speed driving and providing stiffness to the steering handle at the time of high speed driving.
In general, a displacement pump according to the related art using an engine of a vehicle as a driving source was used as a pump for the power steering apparatus of this kind. The displacement pump has characteristics in which discharge flow rate increases with an increase in the number of revolutions of the engine. Therefore, a flow control valve for controlling the discharge flow rate from the pump at a constant amount or less irrespective of the number of revolutions becomes absolutely necessary to use the displacement pump as a pump for power steering apparatus. However, in the displacement pump having such a flow control valve, even when a part of pressure fluid is refluxed to a tank through the flow control valve, a load to the engine did not decrease and an energy-saving effect was not obtained since driving horsepower of the pump is the same.
In order to solve such a problem, variable displacement vane pumps capable of decreasing a discharge flow rate (cc/rev) per one revolution of the pump in proportion to an increase in the number of revolutions have been proposed by JP-A-Hei. 6-200883, JP-A-Hei. 7-243385 and JP-A-Hei. 8-200239. Since these variable displacement pumps are constructed so that a cam ring is moved in a direction in which a pump capacity of a pump chamber decreases in response to a size of a fluid pressure of the pump discharge side when the number of revolutions of an engine (the number of revolutions of the pump) increases, a flow rate of the pump discharge side can be decreased.
Since the variable displacement pumps as described above can relatively increase a flow rate of the pump discharge side when the number of revolutions of the engine is small even during a stop of a vehicle or at the time of low speed driving, in the case of steering during a stop of the vehicle or at the time of low speed driving, large steering auxiliary force can be obtained to perform light steering. Also, at the time of high speed driving of the vehicle, the number of revolutions of the engine becomes large and the flow rate of the pump discharge side relatively becomes small, so that steering in which moderate stiffness is provided to steering operation force at the time of high speed driving is enabled.
Also, in a displacement pump of this kind, it is desired that pressure fluid of a predetermined flow rate be fed to obtain predetermined steering auxiliary force at the time of steering (when steering is necessary) and also a feeding flow rate of the pressure fluid be set to substantially zero or the necessary minimum at the time of no steering (when steering is unnecessary) from the viewpoint of energy saving. For example, in the case of directly driving the variable displacement pump by the engine of the vehicle, at the time of no steering even when the number of revolutions of the engine is large, the amount of discharge from the pump is unnecessary and when the amount of pump discharge at this time is further decreased, driving horsepower of the pump can be suppressed and it is desired to consider such a point.
That is, in controlling the variable displacement pump of this kind, it is desired that it be determined whether a vehicle is stopping or driving at low speed, middle speed or high speed and whether or not steering is performed at the time of the driving and the optimum pump control be performed in response to a driving state of the vehicle. Therefore, it is necessary to take some measures plus an operating state of the pump or a driving state of the vehicle so that the driving state and steering state of such a vehicle are surely grasped and performance acting as a power steering apparatus is exercised by properly performing pump control and also driving control of the pump is performed in a required state and an energy-saving effect is obtained as the variable displacement pump.
An object of the present invention is to provide a variable displacement pump in which in addition to the configuration of the invention according to the application, it is constructed so that stable steering force in the vicinity of the center can be ensured by enabling detection of right and left steering directions and a more energy-saving effect can be achieved while improving steering performance.
In the case that operation of the electronic driving device is controlled in response to a steering speed without determining right and left steering directions of a steering handle as shown in the conventional configuration, when steering is performed right or left near to a neutral position of the steering handle, it is considered that steering has been performed continuously though the steering direction has changed right or left and a steering speed is calculated and the electronic driving device is driven and controlled in response to this steering speed, so that a problem that steering becomes light and stable steering force at the time of straight travel cannot be obtained arises.
On the other hand, the present invention is constructed so that it is not determined that steering has been performed in the case of right and left steering sandwiching a neutral position and only when steering with a predetermined angle or more in either right or left direction has been performed, this steering direction is determined and a steering speed in the steering direction is calculated and a discharge flow rate of a variable displacement pump is changed.
According to a first aspect of the invention, there is provided a control apparatus of a variable displacement pump for power steering apparatus, the variable displacement pump having a cam ring swingably supported within a pump body, a rotor rotatably placed within the cam ring, first and second fluid pressure chambers formed at both sides in a movement direction of the cam ring, a urging member for urging the cam ring in a direction in which a pump capacity of a pump chamber becomes maximum, a metering orifice provided at a midpoint of a discharge passage for pressure fluid delivered from the pump chambers, and a control valve including a spool acting in an axial direction-thereof due to fluid pressure difference between upper stream and down stream of the metering orifice, in which operation of the control valve controls the fluid pressure of at least one of the fluid pressure chambers to swing the cam ring, the control apparatus having an electronic driving device for giving thrust in the axial direction to the spool of the control valve and an electronic control device for controlling a driving current of the electronic driving device, in which the electronic control member comprises a steering sensor, the electronic control member determines a steering direction based on a signal from the steering sensor, the electronic control member calculates a steering speed in the steering direction, and the electronic control member controls the driving current of the electronic driving device in response to the steering speed.
According to the invention, since it is constructed so that the steering direction is determined by a pair of the steering sensors and the driving current to the electronic driving device is controlled in response to the steering speed to this determined steering direction, when right and left reciprocating steering is performed in the vicinity of a neutral position of a handle, it is not considered as steering of one direction and a discharge flow rate of the pump is not increased, so that stable steering force can be ensured and consumption energy of the pump can be reduced since there is no response to steering in the vicinity of the neutral position. Stable steering force can be ensured in response to the driving speed.
According to a second aspect of the invention, there is provided a control apparatus of a variable displacement pump for power steering apparatus, the variable displacement pump having a cam ring swingably supported within a pump body, a rotor rotatably placed within the cam ring, first and second fluid pressure chambers formed at both sides in a movement direction of the cam ring, a urging member for urging the cam ring in a direction in which a pump capacity of a pump chamber becomes maximum, a metering orifice provided at a midpoint of a discharge passage for pressure fluid delivered from the pump chambers, and a control valve including a spool acting in an axial direction thereof due to fluid pressure difference between upper stream and down stream of the metering orifice, in which operation of the control valve controls the fluid pressure of at least one of the fluid pressure chambers to swing the cam ring, the control apparatus having an electronic driving device for giving thrust in the axial direction to the spool of the control valve, and an electronic control device for controlling a driving current of the electronic driving device, in which the electronic control member comprises a steering sensor and a vehicle speed sensor, the electronic control member determines a steering direction based on a signal from the steering sensor, the electronic control member calculates a steering speed in the steering direction, and the electronic control member controls the driving current of the electronic driving device so that a rising point of discharge flow rate changes in response to the steering speed and a vehicle speed from the vehicle speed sensor.
According to a third aspect of the invention, there is provided a control apparatus of a variable displacement pump for power steering apparatus, the variable displacement pump having a cam ring swingably supported within a pump body, a rotor rotatably placed within the cam ring, first and second fluid pressure chambers formed at both sides in a movement direction of the cam ring, a urging member for urging the cam ring in a direction in which a pump capacity of a pump chamber becomes maximum, a metering orifice provided at a midpoint of a discharge passage for pressure fluid delivered from the pump chambers, and a control valve including a spool acting in an axial direction thereof due to fluid pressure difference between upper stream and down stream of the metering orifice, in which operation of the control valve controls the fluid pressure of at least one of the fluid pressure chambers to swing the cam ring, the control apparatus having an electronic driving device for giving thrust in the axial direction to the spool of the control valve, and an electronic control device for controlling a driving current of the electronic driving device, the electronic control member comprises a steering sensor and a vehicle speed sensor, the electronic control member determines a steering direction based on a signal from the steering sensor, the electronic control member calculates a steering speed in the steering direction, the electronic control member controls the driving current of the electronic driving device in response to the steering speed and a vehicle speed from the vehicle speed sensor, and the driving current of the electronic driving device is controlled so that discharge flow rate at a time of straight travel during high speed driving is lower than that at a time middle speed driving.
According to a fourth aspect of the invention, there is provided a control apparatus of a variable displacement pump for power steering apparatus, the variable displacement pump having a cam ring swingably supported within a pump body, a rotor rotatably placed within the cam ring, first and second fluid pressure chambers formed at both sides in a movement direction of the cam ring, a urging member for urging the cam ring in a direction in which a pump capacity of a pump chamber becomes maximum, a metering orifice provided at a midpoint of a discharge passage for pressure fluid delivered from the pump chambers, and a control valve including a spool acting in an axial direction thereof due to fluid pressure difference between upper stream and down stream of the metering orifice, in which operation of the control valve controls the fluid pressure of at least one of the fluid pressure chambers to swing the cam ring, the control apparatus having an electronic driving device for giving thrust in the axial direction to the spool of the control valve, and an electronic control device for controlling a driving current of the electronic driving device, in which the electronic control member comprises a steering sensor and a vehicle speed sensor, the electronic control member determines a steering direction based on a signal from the steering sensor, the electronic control member calculates a steering speed in the steering direction, the electronic control member controls the driving current of the electronic driving device in response to the steering speed and a vehicle speed from the vehicle speed sensor, and the driving current of the electronic driving device is controlled so that maximum discharge flow rate at a time of steering during a vehicle stop or low speed driving is lower than that at a time of middle speed driving.
According to a fifth aspect of the invention, there is provided the control apparatus according to one of the first to fourth aspects, in which the electronic control device calculates a steering angle from the neutral position and the electronic control device controls the driving current of the electronic driving device in response to the steering angle.
According to the fifth aspect of the invention, a neutral position of a handle is detected and the steering angle from the neutral position is calculated and, driving of the electronic driving device is controlled, so that steering force does not reduce at the time of holding steering.
According to a sixth aspect of the invention, there is provided the control apparatus according to the first to fourth aspect of the invention, in which wherein a pressure sensor for detecting a fluid pressure in the discharge passage is provided and a discharge flow rate is controlled based on maximum steering speed within a period during which a detection pressure of the pressure sensor is not less than a predetermined.
According to the sixth aspect of the invention, the presence or absence of steering is determined by on-off of a pressure switch to detect that there is in holding steering and the electronic driving device is controlled, so that a reduction in steering force at the time of holding steering can be prevented.
According to a seventh aspect of the invention, there is provided the control apparatus according to one of the first to fourth aspects, in which the electronic control device comprises a G sensor, and a discharge flow rate is controlled based on maximum steering speed within a period during which lateral G detected by the G sensor is not more than a predetermined value.
According to the seventh aspect of the invention, the lateral G is detected by the G sensor to determine whether or not there is in cornering, so that steering force at the time of holding steering does not reduce.
According to an eighth aspect of the invention, there is provided the control apparatus according to the first aspect, in which the electronic control member controls the driving current of the electronic driving device so that discharge flow rate decreases as vehicle speed increases.